gg
and sperm-cells of their parents. There is no way out of the
difficulty except the one Darwin pointed out. He himself did not find
the solution of the riddle at once. At first he believed that the case
of the workers among social insects presented "the most serious
special difficulty" in the way of his theory of natural selection; and
it was only after it had become clear to him that it was not the
sterile insects themselves but their parents that were selected,
according as they produced more or less well adapted workers, that he
was able to refer to this very case of the conditions among ants "_in
order to show the power of natural selection_."[40] He explains his
view by a simple but interesting illustration. Gardeners have
produced, by means of long continued artificial selection, a variety
of Stock, which bears entirely double, and therefore infertile
flowers.[41] Nevertheless the variety continues to be reproduced from
seed, because, in addition to the double and infertile flowers, the
seeds always produce a certain number of single, fertile blossoms, and
these are used to reproduce the double variety. These single and
fertile plants correspond "to the males and females of an ant-colony,
the infertile plants, which are regularly produced in large numbers,
to the neuter workers of the colony."

This illustration is entirely apt, the only difference between the
two cases consisting in the fact that the variation in the flower is
not a useful, but a disadvantageous one, which can only be preserved
by artificial selection on the part of the gardener, while the
transformations that have taken place parallel with the sterility of
the ants are useful, since they procure for the colony an advantage in
the struggle for existence, and they are therefore preserved by
natural selection. Even the sterility itself in this case is not
disadvantageous, since the fertility of the true females has at the
same time considerably increased. We may therefore regard the sterile
forms of ants, which have gradually been adapted in several directions
to varying functions, _as a certain proof_ that selection really takes
place in the germ-cells of the fathers and mothers of the workers, and
that _special complexes of primordia_ (_ids_) are present in the
workers and in the males and females, and these complexes contain the
primordia of the individual parts (_determinants_). But since all
living entities vary, the determinants must also